The increasing cost of fossil fuels and other energy sources has motivated the search for ways to utilize more fully and efficiently our available energy. Various sources of heat have been recognized as sources of potentially-available energy, with some examples of such heat being so-called "waste heat" from various industrial or commerical applications, and various sources of heat found in domestic environments. One example of the latter is the heat in a typical home attic, there the temperature is usually hotter than ambient temperature even when the attic is insulated from the living areas of the building. Solar energy is another example of heat energy available at relatively low operating cost to the user, apart from the capital cost of apparatus for collecting the solar energy.
Although the theoretical availability of the foregoing and similar forms of heat energy is well known to those skilled in the art, apparatus for making use of such heat energy has been complex, expensive, and consequently not practical for many applications where the amount of available heat energy could not justify the capital cost of prior art equipment required to convert the heat energy to mechanical energy.